A variety of injection molded parts have been made and used for motor vehicle body and trim parts. For example, bumpers, body panels, doors, filler panels, wheel covers, dashboards, arm rests and other parts have been made via injection molding techniques. Additionally, with regard to vehicle exteriors, bodyside moldings, beltline moldings, roof moldings, window moldings, chin spoilers, and rocker panels, etc. are made via injection molding of PVC or other thermoplastic materials.
In order to provide a painted surface for these parts, film lamination techniques have been successfully employed. In accordance with these processes, a paint film laminate is insert molded with the desired thermoplastic to fuse the film over the injection molded part. The resulting injection molded part is ready for assembly without subsequent painting.
The paint film laminate used in these insert molding techniques may comprise a backing sheet of about 0.020″ in thickness to which paint layers are adhered. Typically, the backing sheet comprises an extruded thermoplastic sheet.
In such paint film laminates, a paint film comprising a cast dried continuous paint coating, is provided over the backing sheet. The paint film may consist of a monocoat, a clear coat over a base coat, or a clear coat and a base coat with interposed print or design. The paint film, including base coat, clear coat and print or design, if desired, may range from about 0.5-4 mil. in thickness.
The laminated paint films are available, for example, from a variety of manufacturers. The films are typically provided in a roll, unwound and then trimmed to a proper “preformed” size and shape, ready for insertion into the injection mold. The preform is usually placed along the cavity side of the mold with the painted side thereof facing the mold cavity surface. In some instances, the preform may be placed along the core side of the mold. The mold is then clamped and the desired molten resin is injected into the mold cavity. Heat and pressure conditions in the mold partially melt the backing sheet and a melt bonding or fusion of the injected resin and film occur. Injection molds used for these processes are rear or edge gated so that the molten resin is directed along the backside of the film.
Although these processes provide significant advantage, they are not without problem. For example, edge portions of the part, such as the longitudinally extending edges of elongated strips used for body moldings and the like, may not be completely covered with the film. Accordingly, these edges reveal the uncovered plastic substrate and provide an aesthetically displeasing appearance since the continuity of the printed surface is interrupted by the unsightly appearance of the underlying plastic substrate.
A variety of methods have been developed to cover the edge portions of these co-molded strips. For example, in accordance with U.S. Pat. Nos. 5,599,608 and 5,783,287 (both of common assignment herewith), the paint film is pre-formed prior to the co-molding step so that the longitudinally extending edge portions thereof have re-entrant dispositions relative to the remaining body of the film. Additionally, as set forth in U.S. Pat. No. 5,746,962 (of common assignment herewith), edgewise extremities of the mold cavity, referred to as “pockets,” are provided contiguous to the mold parting line so that, upon co-molding, the desired end of the film positioned in the pocket will be superposed over the molten plastic injected into the pocket. This forms an edge portion of the resulting plastic part wherein the film substantially covers the edge.
The technology reported in the above patents has proven tremendously successful, especially in connection with the manufacture of deep draw or deep dimension parts. However, in the manufacture of relatively flatter trim parts, product reject problems have been encountered due to shifting or rotation of the film in the mold cavity prior to injection of the molten plastic. Additionally, high pressure pinching of the film between the male and female mold platens along the mold parting line also results in undesirable product rejects.
With respect to this latter problem, the high pinching force (usually on the order of about 600 tons) can result in a serrated or feathered edge appearance of the film laminate along the edge of the plastic part thereby leading to the requirement of an additional labor-intensive product trimming step so that the product can comply with stringent product quality standards.